1. Field of the Invention
The present invention, in general, relates to medical prosthetic devices and, more particularly, to self-propelled wheelchairs.
Wheelchairs are well-known devices that are used by those suffering from many types of infirmities that prevent or impede their mobility.
There are two basic types of wheelchairs; manually propelled and self-propelled. Manually-propelled wheelchairs are used by those who generally still retain some hand and arm capability sufficient to propel the wheelchair.
Self-propelled wheelchairs are used by those with limited personal ability to propel the wheelchair. These types of users typically include those people who have some type of a spinal injury, for example those who by their injury are either paraplegic or quadriplegic.
Others who suffer from amputations and other injuries or infirmities that restrict their ability to manually propel a wheelchair may also use self-propelled types of wheelchairs.
Additionally, those who like to travel extended distances on their wheelchairs, for example to a neighborhood grocery store, may lack the stamina to use a manually propelled wheelchair for longer distances. This is especially true when they are returning with groceries and must now transport an increased weight.
Others who like to go for extended “walks” either alone or with ambulatory friends may find that they cannot maintain a reasonable pace if using a manually propelled type of wheelchair. Accordingly, they may prefer to also use a self-propelled type of wheelchair.
The use of self-propelled wheelchairs is based generally on matters of necessity or of preference. However, the use of a self-propelled type of wheelchair is always intended to augment quality-of-life issues for the user.
The instant invention appertains to improvements in self-propelled types of wheelchairs. These are also generally referred to a “power” wheelchairs or “powered” wheelchairs. They may also be referred to by other names. The discussion hereinafter is directed to self-propelled (i.e., powered) types of wheelchairs.
Ideally, a wheelchair should provide maximum mobility under the widest range of circumstances. The user should feel comfortable in his or her ability to maneuver the wheelchair whether inside or outside, on carpet, tarmac, concrete, gravel, or dirt. This is the ideal. The greater the comfort of the user, the greater use will be given to the wheelchair. Accordingly, quality of life will be respectively improved.
However, certain design parameters have heretobefore limited the versatility of prior art types of wheelchairs. As a result, compromise in versatility and applicability has been the norm for wheelchair users. Wheelchair designers have had to make a primary decision as to whether the wheelchair will be used primarily inside or outside. On this basis, compromises in the design of the wheelchair were made that augmented its intended primary application but which also detracted from other applications.
It is from a more intimate understanding of the problems that those who must use wheelchairs experience that a corresponding understanding of the design compromises that prior art types of wheelchairs have been forced to make can occur. It is also only from that same understanding that the benefits of the instant invention can be fully grasped and appreciated.
Therefore, it is necessary to discuss both the needs of the (self-propelled type of) wheelchair user, in particular those persons suffering from spinal injuries and other infirmities that greatly restrict the user's mobility, along with the limitations inherent with prior art wheelchair design.
For example, it is virtually certain that the wheelchair will, at times, need to be used inside a domicile. The person using the wheelchair will need to maneuver around furniture, approach a dining table, back away from the dining table and rotate the wheelchair to face away from the dining table, then move through corridors, doorways, enter into bathrooms, maneuver about in a typically tight space, and then exit from the bathroom.
When designing a wheelchair for use in a residence (domicile) space constraints become of paramount concern. In particular, the turning radius of the wheelchair becomes an important consideration as well as the location of a vertical axis (or axes) about which the wheelchair pivots or sweeps.
Wheelchairs turn primarily by differentially driving a pair of drive wheels in opposite directions as controlled by a joystick or other input device. Depending on the severity of injury or infirmity and the limitations so caused, even the use of a joystick is not an option for some spinal injury (and other) sufferers. Therefore, other types of sensors have been designed to respond to various types of motion that the user inputs into the sensors. These types of inputs are generally known.
While the instant invention is applicable for use with both joystick and other types of input, it is important to understand and appreciate that the wheelchair turns in response to an input provided by the user. This input may be proportional to the subtle motion of a joystick or it may be somewhat crude in nature. Regardless, the ability of the wheelchair to carve a tight circle (i.e., to have a short turning radius) is especially advantageous to use indoors.
Similarly, the indoor wheelchair needs to be low enough to pass under a dining or kitchen table. An inch lower seat height can make a difference in versatility. Similarly, the narrower the width of the wheelchair, the easier it is to pass through narrow doorways. In any given home, certain doors tend to be wider than others, for example main entry doors, while other doors tend to be narrower, for example closet doors and bathroom doors.
If the wheelchair is wider than the opening, then the opening must be expanded at substantial expense or passage becomes impossible. This clearly affects quality of life.
Similarly, corridors can be narrow with “L-shaped” turns that tax both the width of the wheelchair and its turning radius.
Many of the issues that relate to use in a domicile apply to use in public buildings. These issues tend to be amplified in public and wheelchair users can become sensitized. For example, they may become reluctant to dine at a favorite restaurant because their wheelchair is too high to fit under the dining table or because its turning radius carves such a large arc that the user is apt to strike the chairs of those sitting at nearby tables.
Similarly, the width of the chair can become an issue when entering bathrooms, passing down narrow corridors, and in other areas. While many businesses and public facilities have improved their handicapped accessibility, travel into unknown areas can present significant challenges to the person in a wheelchair. In general, whenever a user goes into an unfamiliar public place, at least some apprehension is apt to occur.
It is important to remember that spinal injury sufferers and those with other limiting infirmities have little or no physical capability. They may find themselves totally dependent on the maneuverability of the wheelchair, or lack thereof. They may not be able to manually push an object away from them or urge themselves in any way. This heavy reliance on the ability of the wheelchair also affects their willingness to venture out into the unfamiliar and unknown.
It is also more serious than that. A person who becomes wedged (i.e., jammed) in an opening leading into a bathroom, for example, (and whom is otherwise not ambulatory) is likely to experience fear, even panic. They can literally become stuck until someone arrives to help. They cannot eat, sleep, or sanitarily relieve themselves. If no one is coming for days, the situation can become critical, even when inside ones own home. While this type of scenario is not especially likely to occur when there is sufficient planning and support in place, it is well to keep in mind the seriousness of needs that such users can experience. This growing appreciation helps in understanding the quality of life issues that confront wheelchair users.
Clearly, quality of life is influenced by the wheelchair's ability to maneuver in tight interior areas.
It is also important to be able to use a wheelchair outside. It is not practical and for some it is impossible to vacate one wheelchair designed for inside use and enter into another wheelchair that is better designed for exterior use without also receiving assistance from another person. Often, that assistance is simply not available.
However, when wheelchairs that are designed for interior use are used outside, they can become unstable or get stuck. This is a very serious problem and can even be potentially life-threatening.
With self-propelled wheelchairs they tend to either be rear-wheel drive, front-wheel drive, or mid-wheel drive. With rear-wheel drive units, the drive (i.e., motor driven) wheels are in the rear of wheelchair and a pair of castors in the front of the wheelchair articulate to accommodate turns. With front-wheel drive wheelchairs, the opposite is true. With mid-wheel drive wheelchairs, the drive wheels are located somewhat more central to the wheelchair, with articulating castors in the front and/or rear.
When these types of wheelchairs are used outside, they may be used on concrete, tarmac, tar macadam, gravel, dirt, even soft or slightly muddy soil, such as in nature trails. They are used on level grade, going downhill, and uphill as well.
When used on hard exterior surfaces, traction and stability on a level grade is generally good. However, when going down or uphill, there is a shift in the center of gravity. When used on gravel, dirt, or soil, traction becomes an issue, as is described in greater detail hereinafter.
For example, with a front-wheel drive type of wheelchair when going downhill there is shift in the center of gravity that places a greater proportion of the weight onto the front, or driven wheels. This tends to promote traction. However, it lessens the amount of weight that is disposed on the castors which can affect stability and control of the wheelchair.
When going uphill, the shift in CG (center of gravity), places a greater proportion of weight onto the rear castors, resulting in a loss of weight, and therefore traction, by the front drive wheels. This can easily cause the front drive wheels to spin. If they spin just momentarily, there is the likelihood that they will create a recess or groove in the gravel or soil, thereby utterly losing all motive force. The wheelchair becomes suddenly stuck in a moment's time.
To the paraplegic or quadriplegic, this is a terrifying experience. They can be stranded outside somewhere between their home and a mailbox, on a nature trail, or elsewhere without help or assistance for an indefinite or prolonged period of time. They are subject to sunstroke, dehydration, hypothermia, hyperthermia, as well as considerable psychological and physical distress.
Whenever there is a loss of traction by any of the four wheels (two driven, two castors), there is an accompanying loss of directional control that also occurs. The wheelchair can abruptly change direction without user control. It can veer off the path, down into the woods, possibly causing great physical harm or psychological distress to the user. It is not unlike what an automobile driver would experience if there were a sudden loss of directional control while driving. The experience is terrifying, only more so to the person who is wheelchair-bound because he or she is either greatly limited or unable to leave the scene of the accident and get help.
The same issues also arise with a rear-wheel drive or mid-wheel drive type of wheelchair. There is always the risk that a driven wheel or wheels can spin in loose soil or gravel and lose traction or that a change in the center of gravity can cause a weight shift that results in a loss of stability or directional control by creating an imbalance in the weighting of the wheels.
Sometimes, to increase stability and directional control, spring loaded castors are used either in the front or rear of the wheelchair. Typically, articulating castors are used in the front and non-articulating possibly spring-loaded anti-tip castors are used in the rear. Other variations are possible. However, if the castors include springs that are relatively soft, there is always the possibility that the wheelchair can tilt excessively. This is because the “soft” castors may not provide sufficient support to retain the center of gravity within desirable limits when traversing a steep-enough incline.
Needless to say, it would be terrifying for a user if the wheelchair they were on were to tilt to such an extent that it tipped over backwards while going uphill. Yet this is entirely possible if the center of gravity is displaced too far rearward when going uphill or too far forward when going downhill.
Conversely, if spring-loaded castors are used that include stiff springs (to limit the range of forward and/or backward movement by the wheelchair on grade), then the likelihood exists that the castors (front and rear) will bear a greater proportion of the total weight than is desired. If castors that are not spring-loaded are used, this likelihood is further increased. When the castors bear a greater proportion of the total weight, this, in turn, removes weight from the drive wheels and greatly increases the chance that they will lose traction, spin, and in a moment's time cause the wheelchair to become stuck.
Also, as mentioned before, whenever there is a loss of traction especially for the drive wheels, there is also a loss of directional control. Remembering that steering is accomplished by the differential rotation of the drive wheels, a loss of traction by either or both of the drive wheels makes steering impossible to control.
To overcome these serious issues, certain manufacturers of wheelchairs have provided four-wheel drive types of wheelchairs that include four driven wheels, two in the front on an axle and two in the rear on an axle.
While this is of benefit outside, it clearly becomes a significant impediment if the wheelchair is used inside, and especially if it used on carpet or on throw rugs.
The reason for this can be understood by considering what happens to a four-wheel drive motor vehicle where a non-slip drive train is employed. The system works well on snow and ice and other slippery surfaces when going straight or when turning. However, when such a four-wheel drive vehicle is turned on hard, dry surfaces, a binding occurs between the wheels. This is because the front and rear wheels each track on a different radius and therefore each wheel travels a different amount. This causes the application of a greater drive force to certain wheels and a lesser drive force to be applied to other wheels.
If a four-wheel drive wheelchair is used inside on a hard surface the same binding will occur when turning. This will make turning of the wheelchair difficult, at best, and it can even prevent the wheelchair from turning. Clearly, this is undesirable.
If the four-wheel drive type of a wheelchair is used inside on a carpeted surface the same binding will also occur when turning. However, it is likely that one or more of the wheels will spin on the carpet, as needed to equalize the forces that are applied to the four driven (i.e., drive) wheels. The spinning can damage the carpet, either by leaving markings or by eroding and pulling carpet fibers out of their jute backing.
If the four-wheel drive type of a wheelchair is used on a throw rug another problem due to binding is likely to arise. When a prior-art type of four-wheel drive wheelchair is used on a throw rug, certain of the drive wheels can spin relative to other of the drive wheels, the same as they are apt to do on carpet.
However, the throw rug is not anchored to the floor as is the carpet. Therefore, the throw rug can wrap around a spinning drive wheel and become entangled. The user is apt to find that the wheelchair suddenly becomes entangled when traversing over a throw rug. This can also cause the wheelchair to become stuck. It may not be possible for the user to reverse motion or to otherwise free the wheelchair from the throw rug that has become tightly bound and wrapped around one or more of the drive wheels while being pinched down, perhaps, by other of the drive wheels.
Other problems in traction and stability (i.e., steering) can also occur. With a mid-wheel drive type of a wheelchair that includes both a front and a rear set of castors, when driven over a swale or when passing over a pothole, one or both of the drive wheels can become airborne with an instantaneous loss of traction, stability, and steering.
Again, if the springs that support any of the pairs (i.e., sets) of castors are too weak, the CG can shift excessively and the wheelchair can tip over, either forward or backward. If the springs are made sufficiently strong to prevent this from happening (or if the springs are eliminated), then at any moment the castors can support the entire weight of the wheelchair (and occupant) and the drive wheels can become airborne.
Also, when both front and rear castors are employed, the sweep of the wheelchair is greatly increased. The sweep is defined herein as the arc that the portion of the wheelchair that is furthest away from the axis of turning (usually midway between the drive wheels) takes. If a mid-wheel drive type of wheelchair is turning about a center point near the center of the wheelchair that is between the two drive wheels, the front castors (usually standard equipment on these types of wheelchairs) will sweep an arc. If the arc transcribed by the front castors were to strike an object, for example a leg of a dining table, the turn could not be completed.
When a pair of optional rear castors is also included in a mid-wheel drive type of wheelchair, they now introduce a rear arc that increases the total amount of sweep, or turning radius that is required.
The rear castors are needed for outside stability, especially when going uphill, but inside they hinder turning and maneuverability in general.
It is important to note also that the mid-wheel drive type of wheelchair was made in response to a potential loss of traction that might occur with either front or rear-wheel drive types of wheelchairs that are used on incline. This configuration helped to keep a reasonable amount of the weight disposed over the mid-drive wheels providing the wheelchair did not tilt (i.e., tip) excessively. The tradeoff that occurred with mid-wheel types of wheelchairs was an increased tendency to tip, especially backward when going up grade.
To counter this tendency, a second set of rear castors (in addition to the standard front castors) was added. And, as mentioned above, this then introduced the problem of a loss of weight on the mid-drive wheels occurring during passage over swales and potholes that could place all or most of the weight on the front and rear castors.
Also, another problem with rear castors is that they are not visible to the user when turning. Accordingly, the user is more apt to strike objects with them. Front castors are regarded as far more desirable than rear castors for turning because the user can see the maximum sweep (i.e., arc) that the front castors will navigate while turning. If any impact with an object, such as a dining table leg, is imminent, the user would stop the turn and otherwise attempt to maneuver out of the area. With rear castors, their sweep is not visible and, accordingly, the user impacts objects. This can damage the objects impacted. It also jolts and frightens the user.
Accordingly, there exists today a need for a powered wheelchair that helps to ameliorate the above-mentioned problems and difficulties.
Clearly, such an apparatus would be especially useful and desirable.
It is also to be understood that many types of wheelchairs, not mentioned herein, are available with many other options and features. For example, a desirable feature that is available on certain brands and on certain models of wheelchairs includes a mechanism for raising the seat and helping therefore, to raise the person from a seating position into a more standing position.
This is useful (on level, stable surfaces) when people are gathered together in, generally, a standing situation, such as during parties and other social gatherings. It provides the person in the wheelchair the opportunity to converse with others at face level. This helps to lessen the differences and barriers to conversation that arise between the ambulatory person and the person in the wheelchair.
However, when a wheelchair includes the option of elevating the person into a standing position, it also urges the person forward. This, in turn, moves the CG forward, placing more of the weight on the front castors. Generally, the types of wheelchairs that are able to provide this capability do not include front wheel drive. They are primarily mid-wheel drive units.
This forward movement of the CG when raising the person into a standing position requires that the front castors be substantially rigid. If they were spring loaded, especially if the springs were soft, then there would be a pronounced tendency to tilt the chair forward as the CG is displaced forward. This could then expel the standing person from the chair. Clearly, this is undesirable.
Accordingly, if the standing capability is desired, then a very stiff or rigid front pair of castors are required to maintain the wheelchair in the same plane whether the person is seated (while on a level grade), during raising of the person, and after the person has been elevated forward and into a standing position. Similarly, when the person is lowered, the same plane that the wheelchair is disposed on must also be maintained.
2. Description of Prior Art
Wheelchairs are, in general, known. While the structural arrangements of the known types of devices may, at first appearance, have certain similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.